The automation of various processes in factories or the like calls for automatic recognition of shapes of objects which are handled in the processes. For example, in an assembly line in which parts are fed one after another the situation arises occasionally where it is necessary to sort them out while automatically recognizing their shapes. The present invention relates to a shape measuring instrument which permits fast automatic measurement of shapes of such objects, and hence is suitable for use in automatic measurement of parts in production-line and various other processing and as a visual sensor of a robot or the like.
Various methods have been proposed for detecting shapes of objects. A description will be given of some of them.
(1) Method using TV cameras
In the case of image sensing of the same object with two or three TV cameras, images created in focal planes of the respective cameras differ according to the direction in which the object is viewed and the distance between the object and the camera. This method senses the shape of an object by computer-processing such differences. With this method, the computer-processing time is appreciably long and the accuracy of measurement is low and is readily affected by the illumination of the object.
(2) Triangular surveying method using laser beam
This is proposed in U.S. Pat. No. 4,567,347 (issued on Jan. 28, 1986). According to this method, a laser beam is projected onto the surface of an object, a spot of light created thereon is picked up by a photosensing device, and the direction of light from the spot is detected based on the position of the image of the spot on the photosensing device. The position of the spot on the object surface is obtained from the detected direction of light and the direction of the laser beam through utilization of the triangular surveying technique, and then the shape of the object is decided using many such measured values. This method is now employed in a visual sensor of a welding robot and is convenient for detecting the shape of one cross section of an object, but takes much time for obtaining the shape of the whole object.
(3) Method using a flat light beam and a TV camera
A bright line of light, produced on the surface of an object by projecting thereto a flat light beam (fan beam or slit light beam), bends following the surface configuration of the object when the bright line is viewed from a direction oblique thereto. This method detects the shape of the object surface by image sensing of such a bright line of light. This method is now also applied to the visual sensor of a welding robot, but is low in the accuracy of measurement and is not suited to measuring the whole shape of an object.
As described above, various methods have been proposed, but each of them has the defect that the computer processing time is long, that the accuracy of measurement is low, or that the shape of an object can be measured roughly but a narrow gap cannot be detected. Moreover, the prior art methods all encounter difficulty in detecting the shape of an object of a given configuration and a gap defined by abutting edges of two objects and cannot simultaneously detect the shape of an object and a gap in its surface.
An object of the present invention is to provide a shape measuring instrument which enables the shape of an object to be measured in a short time and with a high degree of accuracy.
It is another object of the present invention to provide a shape measuring instrument which permits measurement of the shape of an object and a gap in its surface.
Yet another object of the present invention is to provide a shape measuring instrument which permits highly accurate and fast measurement of the shape of an object and a gap in its surface.